Residual impurities in epitaxial layers grown by MOVPE

Abstract

Residual impurities in GaAs and AlGaAs grown using trimethylgallium (TMG), trimethylaluminum (TMA) and AsH3 were studied. The silicon compounds, the typical impurity in TMG/TMA, were considerably reduced by the refinement of the synthesis and purification processes. The epitaxial growth using the highly purified TMG (Si<0.2 ppm) showed that the purity of GaAs epitaxial layers was mainly affected by that of AsH3. In high purity layers (electron mobility at 77 K was 89,000–153,000 cm2/V·s). the main residual donors detected by photothermal ionization technique were germanium and silicon. Germanium was also detected by secondary ion mass spectroscopy in a less pure layer. Carbon acceptors were detected in all the layers through 4.2 K photoluminescence measurement. From these results, it was concluded that the purity of GaAs layers was determined by the donors, germanium and silicon, associated with AsH3 and the carbon acceptor from TMG. The influence of oxygen in source materials on the quality of AlGaAs layers was studied. The quality of the AlGaAs layers was found to be influenced by methoxide (-OCH3) in TMA and still more influenced by oxygen in arsine.